1. Field of the Invention
The invention concerns a blower or fan, in particular for ventilating or, as the case may be, cooling of electronic devices such as personal computers.
2. Description of the Related Art
Conventionally, axial blowers with a flat design have been employed for this purpose, and include a cylindrical ring space as flow channel and diagonally arranged blades. The air thus flows axially through the impeller. Therewith a small pressure differential can result in high volumetric flow. When transitioning to higher pressure differentials, however, instabilities occur, which lead to fluttering or strong turbulence and therewith increasingly to undesirable noise production.
Besides this, radial blowers are known, for example from hair dryers, which can develop greater pressure differential and which can overcome higher resistance to flow. Such fans are however generally unsuitable as components in PC-housings due to the low conveyance volume due to their radial or as the case may be tangential flow of air. Also known are hybrids, known in particular as the so-called half-axial fans, which include a diagonal flow component with blades arranged diagonally in the blade zone. Such fans however also are liable to noise disadvantages in computer applications.
Beginning therewith, it is the task of the invention to provide a fan, which avoids the above-mentioned disadvantages and provides high efficiency with low noise development with respect to efficient ventilation and cooling. Besides this, the design should be suitable for incorporation into a computer housing and meet typical system performance requirements.
The invention is based on the idea, of employing a fan with a radial wheel with diagonal flow path, in order to achieve a broad and suitable working range. In accordance therewith an inventive fan is proposed having the following characteristics:
a blower housing including a guide surface defining the exterior limits of a flow channel,
a hub that is mounted in the blower housing so as to be rotatable about an axis of rotation and that defines the interior limits of the the flow channel,
a rotary drive for the hub which is disposed within the hub,
the blades of the hub are asymmetrically distributed about the periphery of the hub and are configured as radial blades,
the guide surface and the hub, in the blade zone between the leading edge of the blade and the trailing edge of the blade, when looked at in the direction of flow, have a conical or slightly bent and widening shape, and the cross-flow surface area inside the flow channel remains constant or decreases.
Therewith, using a compact axial design, a radial type of operation is achieved. In comparison to axial fans or blowers the direction of blowing is only changed slightly, while with similar volumetric flows a significant pressure boost is achieved. The special design for the guidance of the flow channel diagonally through the impeller results in a continuous impedance curve and makes possible therewith an optimization of the work point over a broad range. In particular, due to the low circumferential speed differences, no noise producing disturbances or interruptions in the flow occur until higher pressures in the upper range of the impedance curve. The system requirements of PC""s conventionally do not lie within this range. In this sense, the longer flow path also has a positive effect.
In order to maintain the flow cross-section approximately constant, the guide surface of the housing should, in the blade zone, be of smaller pitch axially than the hub. Therein it is further of advantage, when the guide surface in the blade zone has essentially the shape of a truncated cone with a cone angle of between 20xc2x0 and 60xc2x0, preferably 40xc2x0, and when the hub in the blade zone has essentially the shape of a truncated cone with a cone angle of between 80xc2x0 and 110xc2x0, preferably 95xc2x0.
For the further reduction of noise production it is of advantage when the cone is parabolic, at least in its crown. It is also desirable, when the entry part of the guide surface is rounded along a radius.
Preferably the entry and exit of the flow channels respectively have opposing radial coverings.
According to a particularly preferred design of the invention the blade trailing edge forms an acute angle of incidence relative to the plane of the exit opening of the flow channel set against the direction of flow. It should be ensured that the angle of incidence is between 10xc2x0 and 20xc2x0, preferably 15xc2x0. Therewith it is achieved, that on the downstream side turbulence and, correspondingly, noise development is minimized.
A further improvement is achieved thereby, that the free or outer blade edges run adjacent the guide surface, maintaining a tolerance gap as necessary for clearance.
For increasing the inlet cross-section between the blades it is advantageous when the blade entry edges extend axially upstream of the hub, projecting out towards the entry opening.
A further improvement in aerodynamic effect envisions that the blade entry edge exhibits a radius of curvature of 1% to 4% as well as a profile thickness of 2% to 8% based on the length of the free blade end (outer) edge.
For driving the impeller there is preferably employed an electric motor designed as an external running motor in a recess of the hub.